A typical range extender is an integral part of a hybrid electric vehicle provided to improve its travel range. For example, U.S. Pat. No. 5,264,764 discloses a hybrid electric vehicle comprising an inverter/motor electric drive system, a vehicle controller, a range extender and a traction battery. The inverter/motor electric drive system is composed of an electric motor and an inverter/motor control unit. In response to a torque command signal generated by a vehicle controller in accordance with a position of a hand or foot actuated speed control actuator, the electric motor produces a rotary output transmitted to road engaging wheels through a transmission. The range extender including an internal combustion engine and an alternator is actuated by a vehicle controller to provide electric power to the inverter/motor drive system and/or the traction battery. The internal combustion engine rotationally drives the alternator that outputs electric power applied to recharge the traction battery or directly to the motor. The inverter/motor control unit is responsive to the torque command signal to provide electric power from the traction battery and/or the range extender to the electric motor sufficient to drive the vehicle at a desired speed.
When the vehicle is coasting, a regenerative signal is produced by the vehicle controller to activate the motor as an electrical generator to charge the traction battery. When the motor is in an energy regenerative state, a requested power signal is generated by the vehicle controller to control the power generated by the range extender so that all energy generated by the motor is used to charge the battery. The range extender is controlled by a range extender subroutine called-up by the vehicle controller.
Another example of a range extender incorporated in a hybrid electric vehicle is disclosed in U.S. Pat. Nos. 6,622,804 and 6,333,620, which describe a series type hybrid electric vehicle including electric motors powered by a battery array, vehicle control unit, an internal combustion engine and a generator driven by the internal combustion engine for charging the battery array. The internal combustion engine is controlled by the vehicle control unit to run continuously during operation of the vehicle. The charging of the battery array by the generator is controlled by the vehicle control unit depending on a driving mode of the vehicle, i.e. in accordance with power output, power consumption and rpm of the electric motors. The power generated by the generator is generally maintained constant but may be decreased if the state-of-charge of the battery array approaches an upper control limit at which the battery array may be overcharged, and may be increased if the state-of-charge approaches a lower control limit at which the battery array would be unable to drive the electric motors with enough torque to propel the vehicle.
Hence, a typical range extender is designed specifically for a particular arrangement of a hybrid electric vehicle, in which the range extender is installed. The range extender is controlled by the vehicle controller to interact with the electric motor of the vehicle. In hybrid vehicles, the electric motor is used primarily for low-speed cruising or to provide extra power for acceleration or hill climbing. When braking or coasting to a stop, the hybrid vehicle uses its electric motor as a generator to produce electricity, which is then stored in its battery pack. Therefore, the electric motor in hybrid vehicles improves fuel economy compared to a vehicle equipped only with an internal combustion engine. Unlike all-electric vehicles, which have a limited travel range and create inconvenience for users by requiring frequent recharging at charging cities, hybrid vehicles do not need to be plugged into an external source of electricity to charge batteries.
However, hybrid vehicles present challenges to be addressed in order to be suitable for widespread implementation. A hybrid vehicle is more expensive than an all-electric vehicle. Emissions caused by the internal combustion engine should be minimized or eliminated. Weight and size of a combination of electric motor and internal combustion engine with its fuel supply are important factors in vehicles such as compact cars and trucks.
Therefore, it would be desirable to create a portable range extender that may be electrically connected to an all-electric vehicle to enable the vehicle to travel longer distances, if necessary. Thus the need exists for a portable range extender operable independently of the controller and motor of an all-electric vehicle. Such a range extender would enable the user to move it from one vehicle to another, and would be able to support vehicles of different types.
Further, to reduce emissions and improve fuel efficiency, it would be desirable to control a portable range extender so as to turn on and off its engine in an automatic mode depending on the voltage of the vehicle battery being charged by the range extender. To make the range extender more user friendly, it would be desirable to control it so as to combine its automatic mode operations with operations in a manual mode enabling the user to perform monitoring and testing of the range extender.